The invention relates to a device for detecting register marks.
In multicolor printing, in order to ensure exact overprinting of separated colors or separations, it has become known heretofore to print register marks in each separation. In order not to restrict unnecessarily the space on a printing material available for a print, and to keep the expenditure for register mark scanning devices low, the register marks are provided with relatively small dimensions along a track in the conveying direction of the printing material. The register mark scanning devices can be positioned transversely with respect to the conveying direction in order to be alignable with the narrow track. In the case of automated positioning devices, the register mark scanning device carries out a search run until the track has been found and the register mark scanning device is aligned with the center of the track. In order to find the track better, it has become known heretofore to use advance marks, which are arranged upline of the register marks and which, in the conveying direction, have a length which is a multiple of the length of individual register marks (note the published German Patent Document DE 42 18 764 A1). In spite of these advance marks, the duration of the search and the positioning is relatively lengthy, so that a relatively large number of deficient prints have to be produced until register control can be carried out using the register marks.
It is an object of the invention to provide a device for detecting register marks which permits rapid positioning of a register mark detector, so that the number of deficiently produced prints are reduced.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for detecting register marks, comprising at least one receiver for scanning register marks along a track disposed in a direction of movement of the register marks, and a device for positioning the receiver transversely with respect to the track, in order to determine an offset of the receiver with respect to the track, at least one positioning mark being disposed upline of the register marks in the direction of movement thereof, the positioning mark having at least one edge extending at an angle to the track, having an extent transverse to the track, which is a multiple of the extent of the register marks, and having a predetermined positional relationship to the track which is transverse to the track.
In accordance with another feature of the invention, the positioning mark is formed as a right-angled triangle having one adjacent side thereof disposed in the direction of movement of the register marks.
In accordance with a further feature of the invention, the adjacent side disposed in the direction of movement of the register marks is aligned with a center line of the track.
In accordance with an added feature of the invention, the track is located at an edge of a printing material, and the other adjacent side of the triangular positioning mark extends at least approximately to the edge of the printing material, starting from the center line of the track.
In accordance with a concomitant feature of the invention, in the direction of movement of the register marks, at least two reference lines are producible in the vicinity of the positioning mark.
Due to the provision of a specific positioning mark, which is produced in a defined position in relation to the register marks, a position-dependent signal can be derived, from which the distance of the receiver from the register mark track can be calculated. This distance is available after only one scan of a positioning mark, and the positioning of the receiver can be carried out without delay. The only precondition is that the receiver should also register the positioning mark at the start of the positioning operation, which is readily provided by the large lateral extent of the positioning mark. The starting position of the receiver can be predefined by an entry from an operator. In another embodiment of the invention, the starting position in the case of a known printing-material format can be defined as a distance from a lateral printing-material edge.
It is also noted that the invention is applicable either to printing on sheets or webs.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for detecting register marks, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: